1. Field of the Disclosure
The present disclosure relates to synthetic enamel and bone. In particular, the present disclosure is directed to the production of ordered structures of hydroxyapatite and/or fluorapatite nanorods.
2. Related Technology
Dental enamel is the outermost layer of the teeth. The fully developed mature dental enamel is made of enamel prisms, highly organized micro-architectural units, which consist of bundles of nanorod-like calcium hydroxyapatite (HA) crystals arranged roughly parallel to each other. This structure spans the entire enamel thickness and is likely to play an important role in determining the unique physico-chemical properties of the enamel.
Dental caries is a widespread, chronic, infectious disease experienced by almost 80% of children in the US by the age of 18 and by more than 90% of adults. Such a phenomenon is not restricted to the U.S., and has spread beyond all national boundaries. Caries is, in fact, considered to have a multifactorial etiology. The most prevalent way in which dentists treat carious tissue is to remove it surgically, resulting in an extensive cavity and loss of structural integrity of the tooth. The current standard of care for carious lesions in the dentin is invasive operative treatment. This means removal of all carious dentin (removal of all diseased tissue) and replacement by a restoration to restore form, function, and integrity of the tooth. The greater number of replacement rather than new restorations also suggests that existing techniques have only limited success and that there will be an ongoing need for restoration of carious lesions, whether primary or secondary in nature. This operative treatment option is time-consuming to both dentists and patients, and costly. World-wide, the placement, replacement, and repair of restorations in teeth account for anywhere from 30-70% of a dentist's activity. In order to reduce the cost of oral care to both the patient and governmental bodies, new anti-caries restorative products and materials must be developed.
Nanotechnology has been studied extensively in the past decade for the preparation of nano-scale structures with specific size, shape and physico-chemical properties. It has also created many ways to direct the assembly of nano-particles and one-dimensional nano-scale building blocks, such as nanotubes, nanowires and nanorods, into novel functional superstructures. Among them, the application of surfactants as reverse micelles or micro-emulsions for the synthesis and self-assembly of nano-scale structures has been one of the most widely adopted methods. The application of surfactants has been used to prepare and control the size and shape of nanostructures of chemical compositions, such as barium chromate, calcium phosphates, barium sulfate, cadmium selenide, gold nanorods, and tellium nanorods. These studies have been focused on the application of surfactants for making nanostructures of uniform shape and size. In some cases, these synthesized nanostructure assemblies have an ordered arrangement. For example, nanorods may be capable of self-assembly into smectic-like arrays or liquid crystalline assemblies by solvent evaporation, as described below.
Recently, attempts have been made to assemble one-dimensional nanowires and nanorods directly into organized superstructures with the assistance of surfactants. Kim et al (Kim et al., J Am Chem Soc, 123:4360 (2001)) explored the organization of barium chromate nanorods at the water-air interface using the Langmuir-Blodget (LB) technique. The inorganic nanorods were assembled into isotropic, nematic and smectic phases depending on the surface pressure. The same group has also applied the LB technique to assemble silver nanowires into ordered structures by rendering the nanowires hydrophobic through the use of 1-hexadecanethiol ligands.
Synthetic hydroxyapatite has been produced, the crystals of which are macro, irregular, indiscrete, a mixture of sizes and of variable composition.